In a conventional cooling system for an internal combustion engine, the coolant is circulated by a circulating pump through the engine block, through the cylinder heads and to the intake manifold. In an automobile or other land vehicle, the coolant flows from the manifold to the radiator. With a marine engine, which has no radiator, the coolant passing through the manifold is discharged overboard and make-up water is supplied by a seawater pump.
In the past, the thermostat of a marine engine was usually located in the intake manifold. When the engine is cold and the thermostat is closed, the water or coolant will not pass through the manifold, but a small portion of the water will flow through a bypass that returns to the circulating pump so that there is some water flow through the engine block.
It was believed in the past that it was desirable with a cold engine to heat the manifolds to reduce condensation and prevent any such condensation from flowing back into the cylinders. Thus, with the cooling systems of the past, the cooling water was not flowed through the manifolds until the engine was heated and the thermostat opened.
More recently a cooling system has been employed with marine engines utilizing a thermostat housing assembly such as that shown in U.S. Pat. No. 5,121,787. While that patent is directed specifically to an evaporable foam pattern for producing the thermostat housing, the cast housing is identical in configuration to that shown in the patent. With the construction shown in U.S. Pat. No. 5,121,787, the thermostat is located in a thermostat housing which is mounted to the engine block. As described in U.S. Pat. No. 5,121,787, sea water is pumped into an inlet in the thermostat housing and when the thermostat is closed, a portion of the incoming water is directed through a pair of outlets to exhaust elbows while a second portion of the incoming sea water is circulated through the engine block. When the thermostat is opened, a portion of the returning water in the circulating system will flow to the manifolds. With the arrangement as described in U.S. Pat. No. 5,121,787, no coolant is distributed to the manifolds until the engine warms and the thermostat is open.